The present invention relates to a magnetoresistive head and a read/write separation-type magnetic head, and more particularly, to a magnetoresistive head with a stacked-type pinned layer.
The use of spin-valve magnetoresistive sensors in read-only magnetic heads is increasing the tendency towards further improvement of magnetic recording devices in recording density in recent years. Spin-valve magnetoresistive sensors are basically constructed of a ferromagnetic layer called the pinned layer, a ferromagnetic soft layer called the free layer, an electroconductive layer directly adjacent to and interposed between the above two layers, and an exchange-coupled layer coming into direct contact with the pinned layer. An antiferromagnetic material is usually used for the exchange-coupled layer. Each such sensor also has electrode members that pass an electric current through the above layers, and a vertical-bias layer that applies a vertical-bias magnetic field for suppressing noise (called the Barkhausen noise) due to the nonuniformity of free-layer magnetization. The vertical-bias layer usually uses a Co-based permanent magnet film. The sensor is provided in a very small space (called the reading gap) interposed between two ferromagnetic materials called the magnetic shields. Thus, a magnetoresistive head is constructed and the magnetizing signal of a recording medium is reproduced with high resolution.
The pinned layer has its magnetization fixed in a direction perpendicular to the side facing the recording medium (i.e., the air bearing surface of the magnetic head), and does not change its magnetization direction with respect to the magnetic field of the medium or the magnetic field applied to the sensor film during recording. Free-layer magnetization changes in direction according to the magnetic field applied from the recording medium, consequently causing a magnetoresistive change by changing the angle formed by the pinned-layer magnetization and the free-layer magnetization. The section reproducing this magnetoresistive change as a signal is the spin-valve-type head (magnetoresistive head).
The exchange-coupled layer is adjacent to the pinned layer and applies a strong bias field thereto. This bias field fixes the magnetization of the pinned layer, thus preventing its magnetization direction from suffering changes due to the magnetic field applied from the recording medium or the magnetic field applied from a recording head. The exchange-coupled layer is usually formed using an antiferromagnetic material, and the exchange-coupling magnetic field applied to the pinned layer in the operating temperature range of the sensor needs to be strong enough. A binary alloy with a 1:1 composition of platinum (Pt) and manganese (Mn) is primarily put into practical use to satisfy the need.
The foregoing exchange-coupled layer needs to have a film thickness of about 60 nm to augment the exchange-coupling magnetic field, and that is one of the reasons why the length of the reading gap cannot be reduced since high-density read/write operation must be ensured. Magnetoresistive heads having a structure not including an exchange-coupled layer adjacent to a pinned layer are disclosed in Patent Document 1 (U.S. Pat. No. 5,583,752) and Patent Document 2 (Japanese Patent Laid-open No. 2000-113418).